1. FIELD OF THE INVENTION
This invention relates to a trim press for severing articles from a sheet of thermoplastic material in which articles have been differentially pressure formed and more particularly to a trim press including stationary and movable trim dies assemblies, and dynamically balanced mechanism for moving the movable die assembly in a to-and-fro path of travel toward and away from the stationary die assembly such that the die assemblies periodically engage opposite sides of a sheet of plastic material to sever the articles from the sheet.
2. DESCRIPTION OF RELATED ART
Apparatus, such as that diclosed in U.S. Pat. No. 3,664,791 granted to G. W. Brown on May 23, 1972, has been provided heretofore for successively delivering a heated thermoplastic sheet to a sheet heating station and then to a forming station at which opposed molds engage the sheet to differentially pressure form articles in the sheet. Apparatus constructed according to the present invention is particularly directed to new and novel apparatus for trimming articles such as that disclosed in the aforementioned Brown patent, from the plastic sheet.
Prior art trim presses typically include one stationary platen and one movable platen mounting opposed trim dies which engage opposite sides of the sheet to trim the articles from the sheet. Trim presses have been used for many years for trimming plastic parts formed in a continuous web of material from a forming machine with parts delivered to a horizontal table. Such presses are typically capable of operating at speeds slightly above 100 strokes per minute.
As thermoforming technology improves and thermoforming speeds increase, it has become necessary to run trim presses at higher rates of speeds. Accordingly, it is an object of the present invention to provide a trim press of the type described which has increased trim speed capacity.
It has been found that increased operational speeds can be obtained with appropriate counterbalancing to dynamically balance the moving trim die assembly. Accordingly, it is another object of the present invention to provide a new and novel dynamically balanced trim press.
It is another object of the present invention to provide a trim press of the type described which includes new and novel counterbalancing mechanism for counterbalancing a moving trim die assembly.
In one known attempt to counterbalance a moving die assembly, a balance platen has been mounted on the machine frame for reciprocal to-and-fro movement in a direction opposite to that of the movable. The balance platen was installed between the movable platen and the rotatable drive mechanism and unduly restricted the space available for mechanical ejectors and other auxiliary mechanism. A dynamically balanced trim press is also disclosed in U.S. Pat. No. 4,313,358 issued to Gaylord W. Brown on Feb. 2, 1982. This latter Brown patent, however, discloses two trim die assemblies which are concurrently, oppositely movable toward and away from each other to accomplish the dynamic balancing.
In the prior art trim presses including one stationary platen and one movable platen, the maximum speeds of operation and output are severely limited. Accordingly, it is yet another object of the present invention to provide a new and novel trim press including a stationary trim die assembly and a dynamically balanced movable trim die assembly.
Still another object of the present invention to provide a trim press of the type described including a movable trim die assembly and a drive system for the movable trim die assembly including a counterbalanced weight movably mounted on the frame and a rotatable drive system which is coupled to and concurrently drives the trim die assembly and the counterbalance in opposite to-and-fro directions of travel.
It is a further object of the present invention to provide a trim press of the type described wherein a movable trim die platen and a counterbalance weight are moved in opposite directions via a drive system having a rotatable shaft disposed between the counterbalance weight and the platen.
It is a still further object of the present invention to provide a new and novel trim press of the type described including a movable trim die assembly, a movable counterbalance, and drive system including a drive shaft rotatable on an axis, and a pair of coupling members oppositely eccentrically coupled to the drive shaft for oppositely driving the counterbalance and the platen in opposite directions.
Another object of the present invention is to dynamically balance existing presses without restricting the amount of space that could be used for mechanical ejectors and other auxiliary mechanisms.
Another object of the present invention is to provide an apparatus, for dynamically balancing trim presses of the type described, which is easily constructed and installed and may be retrofitted to existing trim presses in the field without requiring modification of the existing presses and press frames.
It is another object of the present invention to provide a dynamically balanced trim press having a stationary platen and a movable platen which will allow press feeds of up to 175 strokes per minute with existing presses.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.